JSFiddle - React, Tailwind, and code Playground

HTML

<form id="myform">
    <input type="checkbox" name="flag1" checked> Flag 1
    <input type="checkbox" name="flag2" checked> Flag 2
</form>
<button id="update">Update</button>
<div id="output"></div>

JavaScript

var form = document.getElementById('myform');
var inputs = form.getElementsByTagName('input');
var output = document.getElementById('output');

document.getElementById('update').onclick = function() {
    var flags = [];
    for (var i = 0; i < inputs.length; ++i) {
        if (inputs[i].type === 'checkbox') {
            flags.push(inputs[i].name + ': ' + (inputs[i].checked ? 'checked' : 'unchecked'));
        }
    }
    output.innerHTML = flags.join('<br>');
};